1. Field of the Invention
The present invention is broadly concerned with an improved oxygen generating candle having a nontoxic additive compound to smooth decomposition and suppress formation of toxic free chlorine gas. More particularly, it is concerned with a candle having an oxygen source, and having therein an additive taken from the group consisting of the oxides, hydroxides and carbonates of calcium and the rare earth elements, and the hydroxides and carbonates of magnesium, which upon decomposition will yield breathable oxygen.
2. Description of the Prior Art
Chemical oxygen candles based on the decomposition of alkali metal chlorates or perchlorates are used where an oxygen supply is needed in passenger airplanes, submarines, and other closed atmospheric conditions.
Previous oxygen candles have consisted of an alkali metal chlorate or perchlorate source which produces oxygen upon decomposition, and BaO.sub.2 to smooth decomposition and suppress toxic free chlorine gas formation. A metal oxide catalyst is also commonly used to facilitate the decomposition, along with amounts of iron or other metal powder fuel to furnish extra heat necessary to help sustain the decomposition and glass powder or glass fiber as a binder.
Although BaO.sub.2 has useful functions and has been used in oxygen candles for decades, it is a poisonous compound. Unless precautions are taken, tiny BaO.sub.2 particles may contaminate the oxygen produced. Moreover, environmental regulations require costly special disposal of scraps and expended oxygen candles containing BaO.sub.2. Various caustic alkali metal oxides such as Li.sub.2 O.sub.2, KO.sub.2, Na.sub.2 O.sub.2, and Na.sub.2 O have also been used to suppress acidic chlorine gas formation.
Markowitz, in Industrial & Engineering Chemistry Product Research and Development, Vol. 3, No. 4, page 321 at 324, (1964), discloses use of Li.sub.2 O.sub.2 and KO.sub.2 to suppress free chlorine formation in a lithium perchlorate oxygen candle. This reference points out that, consistent with the use of barium peroxide in the chlorate candle and in other pyrochemical oxygen source systems, it is the highly basic additives such as Li.sub.2 O, Li.sub.2 O.sub.2, LiOH, BaO.sub.2 which appreciably lower the amounts of chlorine stemming from the decomposing lithium perchlorate.
U.S. Pat. Nos. 3,702,305, and 3,736,104 disclose use of sodium oxide and peroxide catalysts in a sodium chlorate oxygen candle. However, these alkali metal oxides, as well as those disclosed by Markowitz, are air sensitive and caustic. They will adsorb moisture and CO.sub.2 from the air, resulting in decomposition upon exposure to air, with concomitant problems for production use and storage. Candles using such compounds must be produced by a dry process, and production by wet pressing is precluded. In addition, such candles require costly special disposal when expended or scrapped because of the remaining caustic alkali metal oxides.